<body>
      <!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
      <link rel="stylesheet"
            href="https://stackpath.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css"
            integrity="sha384-HSMxcRTRxnN+Bdg0JdbxYKrThecOKuH5zCYotlSAcp1+c8xmyTe9GYg1l9a69psu"
            crossorigin="anonymous">
      <div class="container">1</div>
</body>